In recent years, multipotent stem cells such as embryonic stem cells (ES cells), induced pluripotent stem cells (iPS cells) and the like (in the present Descriptions, the “ES cell” and the “iPS cell” are generically referred to as “multipotent stem cell”) have been artificially created, and is expected to provide extensive contributions to the fields of the regenerative medicines and the like. Since the multipotent stem cells have pluripotency, in which the multipotent stem cells are capable of being differentiated into various types of cells that constitute the living body, the use of iPS cells of a patient himself/herself allows regenerations of skins, cartilages, bones, vessels, nerves, organs and the like without causing a rejection.
Since the multipotent stem cells have the pluripotency as described above, some of the multipotent stem cells can start their differentiation on the way of the cultivation. It is not possible to restore the cells starting the differentiation in this way back to an undifferentiated state again, and therefore cells in such condition cannot be employed for forming targeted organs and body parts. Therefore, on the occasion of the subculture of the multipotent stem cells, it is critical to ascertain whether or not the colonies of the cultured stem cells are undifferentiated to eventually separate only the undifferentiated multipotent stem cells out.
Identifications of such undifferentiated multipotent stem cells can be achieved by conducting a staining of cells or an observation of fluorescence via employing, for example, “Cell Celector®” commercially available from “AVISO Corporation”. However, in general, the staining process is often conducted after immobilizing cells, and besides, staining agents often exhibit toxic effect for cells, and therefore it is difficult carry out an observation of living cells. Further, even if a staining agent of lower toxicity is employed, such a staining agent is still somewhat toxic to cells, and thus an application thereof to the field of regenerative medicine is not appropriate.